1. Field of the Invention
The present invention relates generally to fluid-filled prostheses and more particularly to a fluid-filled breast prosthesis which can be implanted beneath the skin to replace or augment the female breast.
2. Prior Art
In the field of plastic surgery, it has become a frequent practice to implant a prosthesis in the area of the female breast for reconstruction or augmentation. In the case of reconstruction, cancerous, pre-cancerous or other abnormal or damaged tissue has been removed. This creates a void where the tissue has been removed. A prosthesis may then be inserted through the incision to fill this void. The prosthesis then becomes a permanent replacement for the damaged tissue which has been removed, and its purpose is to restore the body contour to its original configuration. The prosthesis then furnishes support for the surrounding body tissue and organs to preserve as closely as possible the original appearance of the body.
Clinical problems have become apparent with permanent fluid-filled implantable prosthesis. Rippling, knuckling and airage palpation are major problems. Since saline, lacking the visco-elastic properties and memory of silicone gel, transmits fluid waves; ripples, knuckles, and fluid waves are more easily transmitted to the overlying skin. Silicone gel solves many of these problems because its visco elasticity prevents fluid waves.
The problems with saline-filled breast implants are well known in the art. The primary difficulty with such breast implants is that they don't feel like breast tissue. That is, the saline filler is less viscous than breast tissue and sloshes about within the implant giving it a quite unnatural feel. Another related problem is the wrinkling that occurs in the superior portion of a breast implant when the stretchable elastomer outer shell is weighted down by the saline.
Various fillers have been proposed to partially mitigate these problems. Pangman, in U.S. Pat. No. 3,366,975, suggested the use of a plastic form core to fill the breast prosthesis. Pangman's prosthesis comprised a core of plastic foam surrounded by a membrane which is impervious to fluids. The impervious membrane is, in turn, covered by a porous layer to which human tissue can adhere. The core in the Pangman prosthesis prevents wrinkling and is shaped to restore the body to its initial shape and appearance following breast removal. Many of the suggestions of Pangman regarding prostheses design are now incorporated commonly in breast prosthesis. Certainly, the textured outer surface suggested by Pangman to promote tissue ingrowth is a common feature in the outer shell of today's prosthesis. The sponge or foam core has not been widely used for various reasons. One of the reasons is that it is difficult to synthesize a foam which truly mimics human tissue.
Since currently a certain number of patients will not or cannot accept silicone gel implants and desire saline, a shell is needed which will minimize the problems eluded to above. Shells having a cover portion and a reinforced base portion are well in the art. Radovan et al., in U.S. Pat. No. 4,217,889, disclose a shell having a non-extensible base. This base comprises silicone with a fabric or even a metal plate embedded therein to create a stiff, slightly flexible base portion. According to Radovan et al. (Col. 5, lines 40-44), "The cover is preferably relatively thin, on the order of approximately 2020 inch thick, while the base is relatively thicker and reinforced, preferably on the order of about 0.04 inch, with a polyester fabric reinforced embedded therein." Radovan et al. also teach that the difference in extensibility between the cover and the base can be provided by differences in the thickness of the material; the base being thicker than the cover. Thus, while Radovan et al. show the advantage to be gained by reinforcing the base of a tissue expander as, for example, by thickening the base relative to the cover, they do not teach an advantage to reinforcing the cover of the shell (or portions thereof) as, for example, by thickening. Most frequently, shell deformation occurs in the superior (upper) portion of a breast implant. It is desirable to provide a fluid-filled implant which has the safety inherent in water or saline-filled implants, but without the disadvantage of wrinkling or deformation that occurs with prior art saline-filled implants when the wearer changes position.